Former Detective Superintendent Cliff McHardy has sensationally revealed to the Lithgow Mercury and London's Daily Mail that details of the conspiracy were kept quiet so as not to embarrass the Australian Government at the time.

According to The Telegraph, he claimed that the Queen and Prince Philip were travelling across the Blue Mountains towards Orange on April 29 1970 when plotters attempted to derail their train.

The now retired 81-year-old police officer claimed a wooden log was placed on the railway tracks ahead of the monarch's train, but failed when it simply wedged under the wheels and slowed the train down until it eventually stopped at a crossing.

McHardy, who now lives in Glenbrook, said he decided to break his long silence on the case to prompt people to come forward and own up.

It is understood there is no record of the alleged event but the report by the former Lithgow police station chief caused a wild frenzy with the British Fleet Street press inundating Buckingham Palace with demands for details.

A spokeswoman for the Palace this morning declined to comment.

"We are not commenting on an alleged plot that happened 40 years ago," the spokeswoman said.

It is believed the Queen and the Duke of Edinburgh remain oblivious to the alleged assassination attempt to this day. There is no official report of the incident in the UK or Australia. (ANI)